The alignment control system is suited for controlling the angular relationship between two adjacent structures. The system is particularly suited to maintaining the alignment of traveling irrigation systems.
Traveling irrigation systems of the general type described in Boice U.S. Pat. No. 2,711,615 are used widely to irrigate large areas of farmland. A typical system consists of a series of elongated sections placed end to end. Each section consists of a liquid transporting pipe which is flexibly connected at either end to the adjacent sections. The pipes, with or without a supporting structural framework, is supported above the ground on movable carriages with a single carriage under each section of pipe. Each carriage is powered so as propel the section along in a direction applroximately normal to the alignment of the pipe. The assembled sections may be permitted to travel together the length of a field, but are typically driven in a circle about one end of the chain of sections. In such arrangement the central section is fixed to a pivot point about which the system will rotate. The water, carrying any additives desired, is connected to the first section at this point and is distributed through the flexible connections at the section joints to the other sections where it is dispensed through discharge nozzles on each section. Power to operate the carriage drives is also applied at this point and distributed along the length of the chain to each carriage. At the outermost section the pipe is capped and the carriage drive runs on a selected schedule, very often continuously. The interior section runs intermittently to keep abreast of the next outboard section. In this fashion the chair of sections travel about the pivot point approximately radially aligned dispensing the water to a circular area of terrain.
The control system is designed to maintain the alignment of the individual sections with the next adjacent section. Boice utilizes antenna rods which make and break contact with a bare wire which stretches the length of the chain of sections to control the drive motors. Bower U.S. Pat. No. 3,394,729 utilizes a cam actuated switch to accomplish the alignment control. The cam is caused to rotate when the alignment adjacent sections vary. Kinkead U.S. Pat. No. 3.587,763 accomplishes the required control with a duplex switch which is mounted on one section and is actuated by a lever mechanism fixed to the adjacent section. Misalignment of the sections moves the lever which in turn operates the switch to effect the desired control. Sandstrom U.S. Pat. No. 3,823,730 discloses the use of a photodetector or a potentiometer in order to sense and control the misalignment.
Sandstrom discloses a general scheme for control in which an output from a pivotal detector and a separate direction detector are used to trigger a comparator which responds in a predetermined manner to the possible input combinations and operates a motor actuator. The actuator in turn controls the drive motors. Two specific direction detector circuits, one based on the potentiometer sensor and one based on the photodetector, are disclosed each using electronic circuitry. A single electronic direction detector circuit is disclosed wherein the direction is determined from the phase relationship of the power supply line which power the drive motors. A single configuration of an electronic comparator circuit is also disclosed. Sandstrom further discloses an overtravel circuit which monitors the alignment detection signal and energizes a relay to stop the system when the misalignment becomes excessive.
Kinkead suggests that strain gauges sensing tension or compression at the joints between the sections may be utilized in an undisclosed manner in connection with an amplifier to slow down or speed up the drive motor to overcome destructive stresses encountered when the sections are operated on a hillside.